Combine the milk and vinegar in a medium bowl, and set aside for a few minutes so it can curdle a bit (like buttermilk).
To the bowl, add the mayo, lemon juice, garlic, mustard, onion powder, nutritional yeast, salt, several cracks of pepper, scallions, and dill. Whisk the dressing until well combined and relatively smooth.
Taste for seasonings, adding more salt or pepper as desired, or more lemon juice or apple cider vinegar for acidity. I sometimes add an extra teaspoon of lemon juice and a pinch of salt.
If the dressing is too sharp for your taste, add a tablespoon of unsweetened vegan yogurt and stir to combine.
Chill the dressing (my preference), or serve now. Store leftovers in an airtight jar for a week, or longer.